Method of and apparatus for manufacturing load retaining doors



March 27, 1956 c. R. sEABoRNE ET Al. 2,739,635

METHOD OT AND APPARATUS FOR MANUFACTURING LOAD RETAINTNG DOORS Filed Dec. l5, 1952 25 Sheets-Sheet 1 March 27, 1956 c. R. sEABoRNE ET AL 2,739,635

METHOD OF' AND APPARATUS FOR MANUFACTURING LOAD RETAINING DooRs Filed Dec. 15, 1952 5 Sheets-Sheet 2 Z ga@ March 27, 1956 c. R. sEABoRNE ET Ax. 2,739,635

METHOD 0R AND APPARATUS RoR MANUFACTURING LOAD RETAINING DOORS Filed Dec. 15, 1952 s sheets-sheet s doorway opening frame. shown that it is preferable that the reinforcing strapsfbe United States Patent" METHOD F 'AND APPARATUS FOR MAN UFAC- TURINGLOAD RETAIING DOORS Charles R. Seaborne, Appleton, and Stephen J. Bniscll, Kaukauna, Wis., assignors, by mesne assignments, to Signode Steel strapping Company, Chicago, lli., a corporation of Delaware Application December 1s,.19sz,vseria1 No. 325,992 1o Claims. (ci. 154-15) The present invention'relates toa new and improved method of and Aapparatustfor manufacturinglarninated load retaining doorssuch `as are commonly known in the shipping industry as grain doors."

Examples of prior art load retaining or grain doors are disclosed in the patents to Herbert Corkran, No.

2,116,260, dated May 3, 1938, and John M. Moon, No.

2,310,860, dated February 9, 1943.

Grain doors are intended for but a single use, and in ktheir removal from the vehicle or carrier they are de- ;stroyed andthrown'away. Therefore, it is of extreme Aimportance `that their manufacturing costs be maintained Vas `low as possible consistent Vwith the desired lstrength characteristics.

The load'retaim'nggrain doors to which the manufac- .turing method: and apparatus of this invention relate in the interior of a carrieracross the doorway.- opening thereof by nailing the reinforcing straps to theinner facet of the Considerable vexperience thas perforated to serve as locations throughl whichrthesecuringnails may be driven and also to permit the installers to use the nails inserted through the perforations as prys to tension nail the strapping. Nailing kimperforatezstrapping has proved to be unsatisfactory because the `nails too frequently are drivenclose to an edge of the-strapping thereby weakening it,fand sometimes the strapping tears loose under load tension.

It is of courseV obvious that the strapping'andJ enclosing plies of fabric material may be punched: through'zto vprovide. nail holes adjacent the edgesofthe grain door. ."But perforatingl the grain door in such fashion exposes many nail holes through which. the granular material` mayizleak and some granular material isso ne that ak considerable iquantity of it willlpour through small `nail .openingsv almost asreadily as a liquid.

The. copending application of HollinsheadT. Martin tiled December l5, 1952, Serial No. 325,981, and entitled Grain Doorv discloses and claims an imperforate cornposite .grain door which provides an `adequate number ofi perforations or holes through one,.,the inner,.ply'of fabricmaterial and the strapping to-permitnailingithe grain door tothe doorway opening frame.

It is, therefore, theprincipal object of thetpresenti invention to provide a new and improved methodA of and apparatus for manufacturing or fabricatinga load 4retaining` or` grain door having at least two plies, offabricxmaterial, such askraft paper, enclosing a. plurality of transverse reinforcing straps in whichthe strapsandcne vof theplies are selectively perforated and the other, ply .is completely imperforate, thereby providing an imperforate door.

Another-'Objectistoprovidea new' and improved meth i op eration of the latter.

l0d ofmanufacturingfsuch Ia grain door, `which Visf-continuous in its operation and consequently vpermits of fabrication of'grain'doors in substantial quantitiesand yat low-cost.

Anotherobejct is to provide a new andimprovedmethod f of `and apparatus,` for manufacturing a laminatedtgrain door in which the lamination iscarried out in" two-steps and thebonding adhesive is so applied'as not to interfere withcarrying outthe method andnotto befdeposited on theworkingjparts. of the apparatus as to prevent proper 4Other objectsv and vadvantages will become l'apparent from the following description taken in` conjunction with the accompanying drawings, in which:

Fig. l is aperspectiveview'of a load retaining'or grain door manufactured in accordance `with this invention;

Fig.. 2 is a greatly enlarged fragmentary' cross-'sectional View ofthe load retaining or` grain door, taken substantially along the line 2 2 in Fig. l;

Figs 3 and 3a, taken togetherycomprise a schematic diagram of the apparatus of thisk invention on which the door shown in; Figs. l and 2 is adapted' to be fabricated;

Fig. v3b isa view illustrating in elevation the ribbed 'tion .ofthe apparatus'shown inV Figs. I3 and 3a ion which -.a slightlyudiiferentl method of manufacturing' the'door is practised.

.inthe following ,specification the term fgrain'door is used' to 'designate the throw away doors used in carriers such asrailway cars to retainloads of grainsfand other `like bulkshipped commodities.

A grain ldoorS nianufacturedaccording to the present invention isV generally illustrated in Fig. land comprises an inner sheet; or ply of fabric material l5,y such as heavy `kraft paper, and an vouter imperforate` sheet 'or ply '7 ysheets or pliesk 6'and 7 are afplurality of .transverse metallic reinforcingstrapsS whichfmay be madel of cold 'rolled steel. The straps 8 in addition to reinforcing the door -5 also .aidI in effecting a firm attachment of the-door to `4the rdoorway opening. frame of the railway car or other carrier.

.As shown Imost clearly in Fig. .2,v holes'ia care* formed in the-doorS, the holes extending throughtheinnersheet or -ply-.fiandeach of the straps 8, but not throughzthe .outerply or sheet 7 which,v.as pointed out, is imperforate so.as` to. prevent the loss of granular material-,through the holes. These .holesSa are positioned adjacentthe side marginal edges 5a ofthedoor to receive theanails which attach'the'door to the doorway frame of a railway car or other carrier. Since doorway openings are of varying Widths a' number of holesSa are provided iri horizontal spaced relation inwardly from the door'edgesjSa; thus few standard width doors 5 are allE that need bermanufac tured for 'bridging all the 'known doorwayopeningl sizes. Theholes 28a- Aare' longitudinally centrally 'located' in the reinforcing* straps '8 to vobtain the greatest streng'tlrfrom .the reinforcing straps 8. s

.The straps Suare preferablyspaced closer .together-ad jacent the loweredge ofthe door 5 'thanl attheupperxedge so as to provide more reinforcing against thelcunned load at. the,A points-.where it exerts, the. greatest; pressure (Eig-1). f

The manufacture,ofggrain` door.5,y presents certain, difcult problems, because only the inner sheet 6 and the reinforcing straps 8 are perforated while the outer sheet 7 is imperforate. In the above mentioned copending application of Hollinshead T. Martin there is disclosed and claimed the method of fabricating by combining the reinforcing straps 8 with the inner sheet 6 and then selectively perforatlng the combined strap and sheet. The combined and punched sheet and strap are then laminated to the imperforate second sheet 7 and the door is trimmed to the proper size with the nail holes 8a at the marginal edges a. The present invention is concerned with a commercial method of and apparatus for applying the' straps 8 to the inner ply 6, selectively perforating the sheet and strapping, then laminating the second sheet 7 to the combined sheet 6 and strapping 8 to enclose the straps, and finally cutting the laminated plies of paper and strapping to the desired doorway width in a continuous process.

In Figs. 3 and 3a there is diagrammatically illustrated the improved apparatus on which the grain doors 5 may be manufactured in a substantially continuous process. (For simplicity of illustration the machine frame, the driving mechanism and other conventional mechanisms are not shown.) It has been found that the most efficient method of combining the straps 8 with the inner ply 6 is to coat a number of lines of adhesive on the inner face of the sheet 6 equal to the number of reinforcing straps 8 and then to align the straps 8 with the adhesive lines against which they are pressed in the combining portion of the apparatus. The apparatus illustrated comprises an adhesive applicator 10 for coating longitudinally extending lines of adhesive 9 on a continuously moving web of sheet material. The line coated sheet is then passed to a first laminating means 11 where it is combined with superposed continuous steel straps 8 in the area of the adhesive lines 9.

The laminated sheet 6 and strapping 8 are fed to a punching apparatus 12 which is operated selectively to punch gangs of the holes 8a in the laminated strap and sheet material at regularly spaced intervals. After punching, the laminated and punched sheet 6 and strap- .ping 8 are fed to a second laminating mechanism 14 which receives the coated and imperforate sheet material 7 from a second adhesive applicator 13. After passing through combining and cooling rollers, which will be described hereinafter, the laminated product comprising the perforated ply 6 and strapping 8, and the imperforate ply 7 are fed to a shear 15 which cuts the'laminated sheet into sections of doorway width through the center of the gangs of punched holes 8a, thereby completing the doors 5.

From the foregoing it is obvious that the operations of punching the holes 8a and shearing the laminated product into sections of doorway width must be coordinated so that the holes 8a are punched at predetermined intervals and that the shearing is done across the centers of the groups of holes 8a in order that a proper door be manufactured. To this end synchronizing means 16 are provided for coordinating the operations of various portions of the apparatus. As will be more fully explained hereinafter, the synchronizing means 16 include conventional electronic and mechanical apparatus actuated by photoelectric cells which are triggered by marks on the sheet 6 at points spaced apart a distance equivalent to the desired door width.

The adhesive applicator 10 for coating the lines of adhesive 9 longitudinally of the run of the inner sheet 6 comprises a roll 17 having a number of parallel circumferential axially spaced rubber ribs 18 thereon, the number and spacing of the ribs 18 being governed by the number and vertical spacing of the reinforcing straps 8 (Fig. l). The roll 17 is carried on a shaft 17a to lie parallel to the plane of the sheet 6 as it is passed there- 4 the ribs 18 by a pickup roll 20 and a doctor roll 21 from a pool of adhesive 9a in the pan or container 19.

The adhesive may be one of several suitable types and should be chemically inert, moisture resistant and not subject to deterioration if the doors 5 be stored for any length of time. Asphalt type adhesives satisfy these requirements and may be easily handled. Other suitable adhesives include quick setting starch base adhesivest containing chlorinated phenols and adhesives having a silicate base.

If the adhesive be highly viscous, it may be necessary to heat the pickup roll 20, the doctor roll 21 and the ribbed roll 17. It has also been found preferable to have the circumferential surfaces of the ribs 18 on the roll 17 approximately one-quarter of an inch narrower than the width o'f the straps 8. Thus a suicient quantity of adhesive can be coated in lines 9 on the paper, and when the straps 8 are pressed against the sheet to adhere them firmly thereto, little if any adhesive will be squeezed from under the straps to remain on the surface of the sheet 6 not covered by the straps 8. Gumrnng the parts of the apparatus with adhesive is thereby substantially avoided.

The moving web of the sheet 6 is drawn from a supply roll 23 over guide rolls 24a, 24b, and 24e and through a printer portion 62 of the synchronizing means 16 which prints a series of marks 63 (Figs. l and 4) on the outer face of the sheet 6 at spaced intervals equal to the length of the retaining doors 5. As previously noted, the marks 63 are detected by photoelectric cells forming a part of the apparatus coordinating the operation of the punch 12 and shear 15.

After the marks 63 are printed on the moving sheet 6 it travels over a direction reversing roll 25 and under a guide roll 22, the function of the latter beingv properly to locate the sheet with respect to the ribbed coating roll 17.

After the adhesive lines 9 have been coated on the sheet 6 it passes into a nip defined between a pair of oppositely driven combining rolls 26 and 27, and simu1- taneously a plurality of flat steel straps 8 also pass into the nip 28, the number of straps and the spacing thereof transversely of the sheet being dictated by the amount of reinforcement required for the door 5 and coinciding exactly with the number and spacing of adhesive lines 9 coated on the sheet. The steel straps 8 are supplied from a plurality of reels 29 and pass over an elongated guide roll 31 and through levelers 30 which also act as guides Y before entering the nip 28. The levelers 30 remove the over, the shaft 17a being journaled in the machine frame.

Adhesive is transferred to the circumferential surface of curl from the straps 8 so that they lie at against the sheet 6 to insure a good and permanent bond.

If it has been necessary to heat the adhesive 9a before it is applied to the sheet 6, one or both of the combining rolls 26, 27 may be cooled in order `to effect a strong bond between the straps 8 and the sheet 6. When a heated adhesive is employed the strap 8 also cools it so that a rm bond is provided.

From the combining rolls 26 and 27 the'laminated sheet 6 and straps 8 are drawn under a guide roll 32 and into the punch 12 by pull rolls 34 and 35. In order that suitable tension be always applied to the laminated sheet 6 and strapping 8, a dancer roll 35a, carried at the ends of a pair of. arms 35b pivotally mounted to the machine frame and urged downwardly by tension springs 35e connected thereto, rides on the sheet 6 be'- tween the combining roll 27 and the guide roll 32. y

The punch 12 may be one of several commercially available types and may be operated either intermittently or continuously. In the illustrated apparatus the punch is of the ordinary crank type and is intermittently operated by the synchronizing means 16, the inner'sheet and attached strap being fed `into the punch 12,` stopped, punched, and pulled from the punch by the pullrolls 34 and 35. Preferably the punch 12 formsn parallel groups of longitudinally spaced `holes A8a in thefsheet 6 'the adhesive is highly viscous.

and each of the straps 8, each of the groups containing the holes for the trailing edge of one retaining door and the leading edge of the next retaining door .(Fig'. 4). -In order properly to align the combined sheet 6 and's'traps 8 in the punch 12, it may be necessary to trim'anedge of the sheet and provide an edge guide in the punchill, and such trimming may be done between the tension guide roll 32 and the punch 12. However, if the inner sheet is properly trimmed in the tirst instance it has been found `that such trimming is unnecessary.

For the purpose of intermittentlypulling the sheet 6 and combined straps 8 through the punch 12, the pull roll i34 may be moved toward and away from the cooperating pull roll 3S. To accomplish this, the pull roll'34 is carried on a pair of rocker arms 34a supported inter- 'mediate their ends on pivots 34h journaled in the machine frame. The roll 34 is journaled at one end of each arm and the opposite end is mechanically connected to a sole- -noid means indicated generally at 34C which is controlled f by thesynchronizing means 16 so that the roll`34 is lifted when the combined sheet 6 and straps 8 are stopped during the punching operation.

The rocker arms 34a also carry braking means 34d opposite the roll 34, which is actuated simultaneously with the lifting of the roll 34 by the solenoid 34e so that not only is the pulling of the sheet 6 and straps 8 stopped, but the `product is positively iheld during the punching. The brake 34d comprises flat -plates 34e carried on the rocker arms 34a, and when the lbraking means is energized the plates 34e are pressed against a sheet supporting surface 34j carried on the machine frame. Thus the combined sheet 6 and straps 8 vare securely held in the punch 12 through the coaction of the dancer roll 35a and the brake means 34d, because the dancer roll 35a takes up the slack in the combined sheet 6 and straps S ahead of the punch 12. This 'arrangement is important in order to obtain effective punching and overall continuous operation.

After punching, the sheet 6 and straps Strav'el into the second laminating means 14, and a second dancer lroll 37 rides on the combined and punched sheet v6 land fs't'raps 8 between the pull rolls 34 and 35 and this laminating means 14. This roll 37, carried on arms 37a, swingably supported on the machineframe, is Yadapted totake up slack in the combined sheet 6' and Hstraps 8, and usually the weight of the roll will be suf- 'roll43 to a coating roll 44 which transfersadhesive 45a from a pan 4S to one entire'face of the sheet l7 'to form an adhesive coating 5b which firmly bonds the sheet "7 to the straps 8 and the inner face of thesheet r6. The preconditioning roll may be heated if'necessary thereby to condition the sheet 7 for the application of the adhesive. Also the coating roll 44 may be heated if The sheet`7 is lheld in 'contact with the coating roll by a pair of guides 46a and 46b positioned on opposite sides of the axis of ro- `tation of the roll 44, and the adhesive is uniformly spread on the sheet 7 by means of an equalizer or doctor blade -47 which rides against the coated surface of the sheet :7. `Theguide 46h and the third guide 48 assure contact ofthe coated sheet with the blade 47.

In the event that the adhesive is applied while ihot, the laminated product after passing through the laminating rolls 38and 39 passes over cooling rolls 49, 50,'S1,"52 -and 53, each of the cooling rolls being fabricatedffrom l`cast iron'and driven by suitable means in thewe'll known Ameans 16 as in the case'of" the punch 12. -the intermittent operation ofthe-shearlS, the feed rolls 57 Aand`58 are alsooperatedin response to the vcontrol ofthe synchronizing meansf1`6'to feed the laminated 4"mannen The product `passes from 'the cooling rolls through guide'rolls"54,"55 and '56"tofeed rolls 57 and 58 and' then into'the shear 1'5.

` The shear `15 like thepunch 12`may be either intermittent or continuousinoperation In the illustrated `apparatus the shear is `intermittent'in operation, being actuated in response tothe control 'of the synchronizing In view of product into theshear during'the latters nonoperating period and to brake the product during the operating or 'cutting period of the shearlS. As a result lof vthis intermittent feedingof'the"product a slack loop'59 is provided between the guide roll'56 and feed rolls`57 `and 58. Thel slack loop is ten'sioned by 'a'dancer roll l'59a carried on a pairof'arms`59b which are held' against rthe vlaminatedfproduct"under the'tforce of the tension springs 59C.

The'shear 15 maybe `anyfone "of aI number 'of commercially available devices and -`may include a clamp '15b which locks "the laminated product inthe shear'for -the cutting operation. The vvshear cuts off retainingdoors '5-l of' desired width byv cutting'themthrough the centers ofthe parallelgroupsof holes Saso that half of the holes are in the trailing edge of one door 'and the other half ofl these holes are inthe leadingv edge of the next door.

The completed doorsVarecarriedfrom theY shear by la 'belttype conveyorf'tl and deposited in a receptacle 61.

.The synchronizing means,1in addition to including'the zprintinglunit '62 'which printsthe` mark 63 (Fig. l) on .the fo-uter face-of` thefinner sheet at points spaced' apart `4the 'requisite distance, includes a photoelectric cell means e -64`which is'energized` by'. the Arnark'63 and which is assolciated with the tpunch 12 andfpull rolls- 34'and 35. l'lhe photoelectric-cell :isl connected through a control means of a well known type tolactuate the punch 12 and to^'stopv the .feeding ofilthesheet' vand straps 8 by the 4pull rollsk 34fand35. Upon the completion of the punchingoperation'thefimechanism deenergizes the solenoid means-34C and. the. pull rolls '34 and 35 are automatically pressed togetherzto continue feeding the laminated sheet .-6 and straps" 8 to the punch.12.

A` second photoelectric cellmeans 65A is associated with ntheshear 15, vand itis arranged tobe energized by the markr63; it is .included in :electronic and mechanical means of a well known type to actuate the shear 15`and to cause the feed rolls 57.1and.` 55 to stop their feeding operation. After the shear has completed Ycutting the laminated product asabove described the feed rolls 57 and 58 are actuated to resume feeding the product tothe shear 15 a distance equal to thei'width'of another door 5.

AA brief summary' of the operation of ythetapparatus and practice of the method follows: The inner sheet 6 11's fed .from the supply roll23 Athrough the printing unit 62fwhere .the .marks63 are printed.: on thetouter face of the sheet `6. This 'sheet is next coated with .the longitudinally extending `lines 9 of adhesive by 'the ribbed roll 17 and passes into thelaminating means-11 between the laminating rolls 26 and 27. At thesame time a plurality of spaced straps 8 are Vfed from thestrap supply rolls 29 through the. strap levelers' 30 and between the laminating rolls 26.and 27 where they arefbonded to'the `sheet 6 on the adhesive ilines 9. The sheet 6and `com- Abined strapsare pulled bythe pull rolls 34 and 35 under thedancer'roll 35a toguidetroll 32 throughthe punch 1-2. .As .the printed marks-63. pass under the photoelectric cell means 64 the latter operates the synchronizing mecha- Anism` 16 to stop the feeding tof 4therolls 34 and 35,' to energize the vbrake means 34d,-and to operate the punch to form the holes 8a. After punching, thepull rolls 34 .and 35. are movedto their feeding Vposition to draw the punched products from the punch 12'.

The punched sheet .6.and. straps 8 -are pulled' under a second dancer roll 3.7 into the second laminating means 14 and are bonded to the adhesive coated imperforate outer sheet 7 between the laminating rolls 38 and '39. The laminated product is then passed over the driven cooling rolls 49, 50, 51, 52 and 53 and pulled through the guide rolls S and 56 by the feed rolls 57 and 58 which are intermittently operated. The laminated product is fed by the rolls 57 and 58 into the shear 15, the latter being actuated by the energization of the photoelectric cell means 65 in response to its detecting one of the printed marks 63. During the shearing operation the feed rolls 57 and 58 are stopped but are started as soon as a retaining door S has been cut from the leading end of the laminated product. As the doors are cut off, they are drawn from the shear by the continuously moving conveyor 60 and deposited in the receptacle 61 for bundling and shipping.

A modification of the apparatus illustrated in Figs. 3 and 3a is shown in Fig. 5, wherein the adhesive instead of being coated in lines on one face of the sheet 6 is coated on the straps 8. In Fig. 5 those parts of the apparatus which are similar to the corresponding parts shown in Fig. 3 are given the same reference characters. Thus, the sheet 6 is fed from the supply roll 23 through the printer portion 62 of the synchronizing means 16 and over the direction reversing roll to the nip 28 of the laminating rolls 26 and 27 which are shown in a slightly different position than in Fig. 3.

The strapping 8 is fed from the supply roll 29 through the levelers 30 and over a guide roll 66 and around a second guide roll 67 which also reverses its direction so that it properly may be fed to the laminating means 11. The rolls 66 and `67 are located on opposite sides of the coating roll 21 which picks up adhesive from the heated roller 29 which turns in the pool of adhesive 9a in the container 19. The rolls 66 and 67 maintain proper contact of the straps 8 against the coating roller 21 so that one face of each of the straps is continuously coated with the proper quantity of adhesive.

The coated straps are firmly bonded to the sheet 6 in the laminating means 11 and then are pulled by the rolls 34 and 35 to the punch 12. The remainder of the apparatus is the same as or similar to that already described, and the remainder of the process is carried out in the same manner. It will be observed that in this modification of the process the adhesive instead of being coated in lines on the sheet 6 is coated in similar lines on each of the straps 8 which are pressed against the sheet 6.

By either of these processes only so much of the adhesive is applied either to the sheet 6 or to the straps 8 as is necessary firmly to bond the straps to the sheet, and, therefore, no excess quantity of adhesive lies on the sheet 6 between the straps which might gum up the laminating, heating and guide rolls of the apparatus or the punch 12.

It will be appreciated that the process and the apparatus described are effective to manufacture a laminated retaining door of the type shown in Fig. l which comprises an imperforate sheet bonded to a perforated sheet and reinforced by perforated straps, the product being an imperforate load retaining door which may easily -be nailed in place in a shipping vehicle such as a railway car.

While two embodiments of the method and apparatus constituting this invention have been shown and described, it will be apparent that numerous modifications and variations thereof may be made without departing from the underlying principles of the invention. It is therefore, desired by the following claims to include within the scope of the invention all such variations and modifications by which substantially the results of this invention may be obtained through the use of substantially the same or equivalent means.

What is claimed as new and desired to be secured by United States Letters Patent is:

l. A method of continuously manufacturing load retaining doors comprising the steps of feeding a sheet material and a number of parallel spaced reinforcing straps to extend longitudinally of the sheet material, applying spaced lines of adhesive to one of the adjacent faces of the sheet material and the reinforcing straps, pressing the sheet material and the reinforcing straps together so that the adhesive bonds the straps to the sheet material, punching holes through the combined straps and sheet material, and bonding an imperforate sheet material to the combined and punched straps and sheet material over the punched holes.

2. A method of continuously manufacturing load retaining doors comprising the steps of feeding a sheet material and a number of parallel spaced reinforcing straps to extend longitudinally of the sheet material, applying spaced lines of adhesive approximately the width of the straps to one of the adjacent faces of the sheet material and the reinforcing straps, pressing the sheet material and the reinforcing straps together so that the adhesive bonds the straps to the sheet material, punching holes through the combined straps and sheet material, and bonding an imperforate sheet material to the combined and punched straps and sheet material over the punched holes.

3. A method of continuously manufacturing load retaining doors comprising the steps of feeding a first web of sheet material and a number of parallel spaced ribbons of reinforcing straps to extend longitudinally of the sheet material, applying spaced lines of adhesive approximately the width of the straps to one of the adjacent faces of the sheet material and the reinforcing straps, pressing the sheet material and the reinforcing straps together so that the adhesive bonds the straps to the sheet material, punching parallel and longitudinally spaced groups of holes vthrough the combined straps and sheet material, feeding a second and imperforate web of sheet material longitudinally of the combined and punched straps and first web of sheet material, bonding the second web to the first web and straps to enclose the straps therebetween, and cutting the resulting laminated product transversely through approximately the center of the groups of, holes to produce the load retaining doors.

4. A method of manufacturing load retaining doors comprising the steps of applying longitudinally extending spaced lines of adhesive to a sheet material, applying fiat reinforcing straps to the adhesive lined sheet material longitudinally of the material and on the lines of adhesive, punching holes through the combined straps and sheet material, and laminating an imperforate sheet material to the combined and punched straps and sheet material over the punched holes. v

, 5. A method of manufacturing metal strap reinforced load retaining doors comprising the steps of applying longitudinally extending spaced lines of adhesive to a sheet material, the lines of adhesive being approximately strap width, pressing flat reinforcing straps against the adhesive lined sheet material longitudinally of the material and on the lines of adhesive, punching holes through thecombined straps and sheet material, and laminating an imperforate sheet material to the combined and punched straps and sheet material to enclose the straps between the sheets.

6. A method of manufacturing load retaining reinforcing doors comprising the steps of applying adhesive to a number of spaced parallel reinforcing straps, pressing the adhesive coated reinforcing straps against a sheet material longitudinally thereof tobond the straps to the sheet material, punching holes through the combined straps and sheet material, and laminating an imperforate sheet material to the combined and punched straps and sheet material to enclose the straps between the sheets.

7. An apparatus for manufacturing metal strap reinforced load retaining doors comprising means adapted to supply a first web of sheet material, means adapted to supply a number of spaced parallel reinforcing straps longitudinally of the sheet material so as to bring a face of the strap against a face of the sheet material, means coating lines of adhesive on one of the faces of sheet material and straps, laminating rollers pressing the straps and sheet material together to bond the straps to the sheet material, a punch for forming transversely spaced parallel groups of holes in the combined straps and sheet material, drive means for feeding the combined strap and sheet material through said punch, means adapted to supply a second and imperforate web of sheet material, means coating adhesive on one face of the second Web, laminating Arollers pressing the coated face of the second web to the combined straps and first web to enclose the straps between the webs, a shearing means for transversely cutting the combined webs and straps through approximately the center of the groups of holes into sections of door width, second drive means for feeding the combined webs and straps through the shearing means, and synchronizing means controlling the operation of all of said drive means, said punch and said shearing means.

8. An apparatus for manufacturing metal strap reinforced load retaining doors comprising means adapted to supply a rst web of sheet material, means adapted to supply a number of spaced parallel reinforcing straps longitudinally of the sheet material so as to bring a face of each strap against a face of the sheet material, means coating lines of adhesive on one of the faces of the sheet material and the straps, driven laminating rollers pressing the straps and sheet material together to hond the straps to the sheet material, an intermittently operating punch for forming transversely spaced parallel groups of holes in the combined straps and sheet material, intermittently operating drive means for feeding the combined strap and sheet material through said punch and stopping its movement during operation of said punch, means adapted to supply a second and imperforate web of sheet material, means coating adhesive on one face of the second web, laminating rollers pressing the coated face of the second web to the combined straps and rst web to enclose the straps between the webs, an intermittently operating shearing means for transversely cutting the combined webs and straps through approximately the centers of the groups of holes into sections of door width, second intermittently operating drive means for feeding the combined webs and straps through the shearing means and stopping the movement thereof during operation of said shearing means, and synchronizing means controlling the operation of all said intermittently operating means.

9. An apparatus for manufacturing metal strap reinforced load retaining doors comprising means adapted to supply a irst web of sheet material, means coating narrow lines of adhesive on one face of the sheet material, means adapted to supply a number of spaced parallel reinforcing straps longitudinally of the sheet material so as to bring a face of each strap against a face of the sheet material on the lines of adhesive, laminating rollers pressing the straps and sheet material together to bond the straps to the sheet material, a punch for forming transversely spaced parallel groups of holes in the combined straps and sheet material, means adapted to supply a second and imperforate web of sheet material, means coating adhesive on one face of the second web, laminating rollers pressing the coated face of the second web to the combined straps and first web to enclose the straps between the webs, and shearing means for transversely cutting the combined webs and straps through approximately the centers of the groups of holes into sections of door width.

10. An apparatus for manufacturing metal strap reinforced load retaining doors comprising means adapted to supply a first web of sheet material, means adapted to supply a number of spaced parallel reinforcing straps longitudinally of the sheet material so as to bring a face of each strap against a face of the sheet material, means coating lines of adhesive on one face of each strap, 1aminating rollers pressing the straps and sheet material together to bond the straps to the sheet material, a punch for punching transversely spaced parallel groups of holes in the combined straps and sheet material, means adapted to supply a second and imperforate web of sheet material, means coating adhesive on one face of the second web, laminating rollers pressing the coated face of the second web to the combined straps and rst web to enclose the straps between the webs, and shearing means for transversely cutting the combined webs and straps through approximately the centers of the groups of holes into sections of door width.

References Cited in the file of this patent UNITED STATES PATENTS 2,310,860 Moon Feb. 9, 1943 2,372,617 Trew Mar. 27, 1945 2,551,796 Fitzpatrick et al. May 8, 1951 2,559,783 Moon July 10, 1951 2,595,087 Leslie Apr. 29, 1952 2,633,441 Buttress Mar. 31, 1953 

